This invention pertains to the production of chlorine in an electrolytic cell and more in particular to an electrolytic cell system with an improved means of feeding an alkali metal chloride to an electrolytic cell.
When operating a diaphragm-type electrolytic cell to produce chlorine and an alkali metal hydroxide, an alkali metal chloride is generally supplied to or fed into the anode compartment of the cell as an aqueous solution of the alkali metal chloride, such as sodium chloride. To attain optimum recoveries and maximize efficiency of certain diaphragm type electrolytic cells, it is oftentimes desirable to maintain the sodium chloride concentration in the anolyte at near saturation levels. This has been found to be difficult since electrolysis depletes the aqueous anolyte solution of sodium and chlorine ions, thereby increasing the water content and reducing the concentration of the sodium chloride.
It has heretofore been proposed that fine particles of sodium chloride be added to the anolyte to maintain a relatively high sodium chloride concentration within the anode compartment. U.S. Pat. Nos. 1,388,466; 1,388,474 and 1,423,584 describe various means to add solid sodium chloride salt to a chlorine producing electrolytic cell.
Whenever a solid salt is added to an electrolytic cell, over-saturation of the anolyte must carefully be avoided to prevent precipitation of solid salt within the anode compartment and deposition of solid salt on or within the diaphragm. The diaphragm, and thus the electrolytic cell, will become inoperative or at least highly inefficient if the diaphragm becomes plugged due to the deposition of salt particles therein.
An apparatus and method are desired which will permit operation of an alkali metal chloride concentration in the anolyte at near-saturation levels without resulting in oversaturation of the anolyte with the salt, thereby causing deposition of salt in the diaphragm, or deposition of solid salt within conduits leading to the anode compartment.